Sonic method and apparatus for tinning and casting metals



March 5, 1968 A. c. DE WILDE 3,371,703

SONIC METHOD AND APPARATUS FOR TINNING AND CASTING METALS Filed March 30. 1964 v a 20 W W56 {0 3 {Z i 14 22 I m 2? i4 24 g A? w 25 Am i SUPPLY I I I r United States Patent O 3,371,703 SONIC METHOD AND APPARATUS FOR TINNING AND CASTING METALS Andries C. de Wilde, Warren, Mich., assignor to General Motors Corporation, Detroit, MlClL, a corporation of Delaware Filed Mar. 30, 1964, Ser. No. 355,635 5 Claims. (Cl. 164-49) This invention relates generally to the use of sonic Wave energy in the wetting or casting of metal articles and particularly to the casting of metal articles of a composite nature such as a brake drum of the type where an aluminum drum has a bonded cast iron liner.

One problem in the tinning or soldering of metals is the difficulty of creating a good bond between the wetting metal and the base metal due to the oxide film that characteristically forms on bare metal surfaces. Breaking up the oxide film is usually done chemically with a flux that dissolves the oxide so that the solder or wetting metal can reach the surface of the base metal and adhere to it.

In other cases, the presence of an oxide film is of lesser importance since the natural attraction between two metals is great. The wetting of a copper penny wih mercury is an example. Between these two extremes, however, a flux may or may not be required depending upon various factors.

As an example, aluminum brake drums having cast iron liners may be made by machining the cast iron liners and then immersing each liner in a molten aluminum bath at an elevated temperature for several minutes. No flux or other wetting aid is required for this coating process since iron and aluminum have a natural atfinity for each other provided the natural oxide film is not too complete. The

aluminum coated liners are next removed from the bath and inserted in a mold which has a mold cavity the shape of the brake drum being cast. Molten aluminum is cast around the liner bonding to its aluminized surface to complete the drum.

Some of the problems related with this process may also be common to plain soldering or tinning operations. For example, in making aluminum brake drums, the cast iron liners require a soaking time in the bath of about 12 minutes. Iron dissolves in aluminum and contaminates the bath. The iron-aluminum alloy thus formed will not wet cast iron as readily as pure aluminum and the bath must be periodically purified or discarded. The presence of some surface oxides at the iron-aluminum interface weakens the bond. Also, with iron, graphite crystals on the surface of the liner reduce the efiectiveness of the wetting action and the subsequent bond.

Experience has shown that ultrasonic and sonic vibrations may be used to break up oxide layers and aid in the wetting of metals otherwise requiring a flux. A common way of doing this is to vibrate the part to be coated while in contact with the molten metal or vice versa. An explanation for the oxide destruction apparently lies in the fact that there is a mechanical attack of the metal surfaces by tiny bubbles formed on the liquid-solid metal interface due to the shearing action caused by the vibrations. These bubbles collapse against the surface of the base metal causing a break up of the oxide layer by a process called cavitation.

I have discovered that through the application of sonic wave energy and cavitation forces in a torsional vibration system the surface wetting of metals may be tremendously speeded up. In the case selected for illustration of that of a brake drum, the cast iron liner was soaked for 12 minutes to wet it with aluminum and then cast. It is now possible with my invention to wet and cast the liner in one operation in a time of about 40 seconds.

This surprising result is made possible through the use of sonic wave energy. The present application of sonic wave energy is to be distinguished from the type where a vibrator is merely attached to the side of a part or placed in contact with the joint and the parts vibrated. This is brute force shaking and has nothing to do with the present invention.

In accordance with this invention, a torsional vibration apparatus is provided comprising an elastic column which may be in the form of a steel tube having inertia weights connected at opposite ends. At one end, a metal article which is to be coated and/or cast is supported as part of the inertia mass and is suspended in a mold filled with molten metal. A balancing inertia mass is connected at the other end of the tube. A vibratory source capable of imparting oscillatory motion to one of the inertia masses induces an alternating elastic deflection in the column and a similar oscillatory motion in the other inertia mass. The column responds to the vibrational impulses producing a standing torsional wave vibration at the resonate frequency of the system. The oscillatory motion of the inertia masses may be only a few thousandths of an inch at the resonate frequency of the system, but the restoring acceleration forces are of such magnitude that large cavitation forces are developed which cause a vigorous mechanical attack of the metal surfaces to be wetted with resulting disintegration of any oxide layers thereon. The elastic column functions somewhat as a torsion spring with the two rigid inertia masses resonating degrees out of phase.

A more complete understanding of my invention may be had by referring to the following description and drawings wherein:

FIGURE 1 is a longitudinal sectional view through the torsional vibration apparatus showing the mold for casting brake drums; and

FIGURE 2 is a plan view of the apparatus shown in FIGURE 1 with sections broken away showingthe vibrators.

Referring to FIGURE 1, the torsional vibration system 10 includes an elastic column 12 in the form of a metal tube having one inertia mass 14 at the upper end and another inertia mass 16 at the lower end suspended in the brake drum mold 18.

In more detail, the inertia mass 14 is rigidly connected to the upper portion of the column or tube 12 and has a centrally located air delivery line 20 leading from an air pressure source 22. A passage 24 within the inertia mass 14 radiates outwardly from the center at the line 20 and connects with two oppositely located chambers 26 which house the vibrators 28. The vibrators shown are of the air driven hoop-type capable of developing about 1000 pounds of force at 1000 cycles per second, however, other sources of vibrational energy may be used so long as they develop torsional resonance in the system and at the acceleration magnitudes contemplated by the invention.

As seen in FIGURE 2, air under pressure is jetted tangentially from chambers 26 into the chambers 30 through nozzles 32 formed in the stationary ring 34. The air impinges on the surfaces of hoops 36 driving them around the posts 40. Each hoop 36 is of substantially greater inside diameter than the exterior diameter of the associated post 40 and is of lesser outside diameter than the interior diameter of the associated ring 34. Spent air is exhausted through ports (not shown) aligned with chambers 30 in the vibrator covers.

The hoop-type vibrator multiplies the vibrational impulses which can be delivered to the excited mass over that which could be produced by a shaft mounted eccentric for example. In other words, as each hoop makes one orbit about the post 40 inside the ring 34 it may have actually completed only a portion of a revolution itself, thus before one revolution is complete three or four impulses may have been given. This multiplication factor depends on the ratio of the diameter of the post 40 to the inside diam- 3 eter of the ring 36, i.e., as the ratio approaches unity, when the diameters are nearly equal, the frequency step-up relative to the speed of rotation of ring 36 approaches infinity.

The rotating force vectors imparted to the posts by the hoops are transmitted to the inertia mass 14 and then to the elastic column 12. The hoops 36 are automatically synchronized to operate in phase, that is, so that they have their horizontal components of motion in step with one another. It might be noted that due to the relationship of the two vibrators on opposite sides of the center line of the system that the force vectors developed in a vertical plane through the vibrator axes cancel out while those developed perpendicular to such plane will apply an alternating torsional force couple about the axis of the system to produce oscillations in the mass 14 and in the elastic column 12.

Synchronization of the hoops 36 results from their being connected through the other masses of the system. That is, when the hoops are driven at a spin frequency approaching the resonate frequency of the system for a torsional standing Wave vibration, the mass 14, as a result of some initial deflection received from the vibrators, is started into a torsional mode of vibration. As a result of this torsional vibration or oscillation, the column 12 begins to twist back and forth elastically. This incipient vibration tends to begin synchronization of the hoops 36 so that each successive impulse begins to reinforce the oscillations of the system in the direction already begun and as the hoops come into better and better phase relationship as a result of this action, the elastic deflection of the column 12 becomes stronger and stronger. The process builds up until the system vibrates at its maximum amplitude and the hoops 36 are in perfect synchronization.

The lower inertia mass 16 includes in its weight distribution a circular cast iron brake drum liner 44 arranged concentrically with the column 12. A press fitted plate 46 having an axially extending peripheral flange 47 supports the liner relative to the mold cavity. The plate and liner make up the mass unit 16 and are bolted to the bottom of the column 12.

In casting an aluminum brake drum, the cast iron liner 44 is suspended in a mold 18 having a mold cavity the shape of the exterior surfaces of the drum. The mold may be mounted for reciprocatory movement relative to the torsional vibration apparatus 10. When in the position shown in FIGURE 1, molten metal is introduced through the sprue 52 from the bottom and caused to flow radially outwardly beneath plate 46 and upwardly surrounding the liner 44 to the top of the mold. Any suitable means to effect this force feed may be employed. The mold cavity and the side of plate 46 facing the mold cavity may be coated with a suitable mold parting compound to insure release upon cooling.

With the mold in a raised position, the torsional vibration apparatus is brought to resonance. The molten metal is introduced into the mold through the sprue 52 rising between the mold cavity and liner to the top of the mold. The liquid metal will have a dash pot effect on the vibrating system tending to dampen the oscillation. However, before the system is completely detuned, the cavitation forces at the outer surface of the liner 44 exposed to the molten metal will cause incipient wetting to occur in about 20 seconds and complete casting of the brake drum may be accomplished within 40 seconds upon cooling. This one step process is contrasted to the two step operation commonly in use, that is, wetting the liner and-then casting the drum. There the soaking time required for wetting the cast iron runs to as much as 12 minutes. Also, the separate casting operation requires the liners to be handled a second time before a complete drum is made.

The cavitation forces produced at the resonant frequency of the system are so great that care must be exercised to prevent the surface of the cast iron liner from dissolving. Accordingly, the destruction of the surface oxide layer is so complete that an excellent bond is formed in a few seconds without the use of a flux.

The magnitude of the cavitation forces is dependent on the power of the vibrator and operation of the system at the resonate frequency. With the vibrators shown, large deflections or amplitudes are possible at acceleration levels many times the acceleration of gravity. For example, a 250 c.p.s. torsional vibration system of the type shown will produce rim deflections of about 0.008 inch in air. The acceleration levels are lower in molten metal than in oil or water, however, in spite of the resistive detuning of the system with molten metal, there is more than sufficient activity to produce wetting.

After casting, the mold is lowered and the sprue stock and adjacent metal filling in theplace of the axle opening of the drum is knocked off according to cast in fracture lines. The plate 46 is unbolted and separated from the liner 44 and the apparatus made ready for the next casting operation.

If it is found desirable to add heat during the casting process to prolong solidification, this may be done by gas burners applying heat to the mold surfaces or by an induction coil arranged radially inwardly of the liner 44 for example.

Instead of plate 46 to maintain the liner 44 in spacial relationship with respect to the mold cavity, some type of clamp may be devised which could be hydraulically connected and disconnected.

Obviously, the invention can be applied to the wetting of the ends of bars, tubes, or other generally annular bodies where torsional vibrations could be exepected to produce strong, uniform cavitation forces at the metal surfaces. Torsional vibrations have particular utility in the field of casting brake drums where wetting of the cast iron liner was a necessary step prior to casting, however, it should be understood that in casting almost any composite article, the inventive apparatus can be easily adapted for use.

Having now described the invention in the most preferred form, it should be clear to those skilled in the art that obvious modifications can be made without deviating from the scope of the appended claims except insofar as limited by the prior art.

I claim:

1. A method of wetting a metal surface with a molten metal comprising the steps of:

torsionally vibrating an elastic column producing a standing wave vibration at the resonate frequency thereof causing alternating torsional deflections to occur at opposite ends of said column, the deflection at one end being generally degrees out of phase with the deflection at the other end at the resonate frequency,

supporting said column at the nodal point where torsional deflection is at a minimum,

supporting a metal body at one end of the column so that it receives oscillatory excitations therefrom, placing said body while in said oscillating condition in a container, and introducing molten metal into the container to mechanically attack and wet the surfaces of said body as a result of the shearing action between the molten metal and body surfaces.

2. The method according to claim 1 wherein the container is a mold cavity for forming a composite cast article and said metal body surfaces define other surfaces of said article with the mold cavity, the step in addition of detuning the elastic column by the damping action caused by the solidification process whereby the metal body forms an integral part of the cast article.

3. Sonic vibratory apparatus for wetting the surface of a ferrous metal article located in a bath of molten non-ferrous metal, comprising an elastic member, vibration generating means connected to said elastic member, a source of compressed air for driving said vibration generating means at a resonant standing wave frequency of said elastic member so as to establish at least one nodal point and one antinodal point along said member, a coupling member extending from said elastic member at an antinodal point thereof, and means for supporting said elastic member so that said coupling member is located in said bath for delivering high frequency vibratory energy to the molten non-ferrous metal adjacent said surface of said article.

4. Sonic vibratory apparatus for Wetting the peripheral surface of a ferrous metal brake liner located in a bath of molten non-ferrous metal, comprising an elastic member, vibration generating means connected to said elastic mem ber, a source of compressed air for driving said vibration generating means at a resonant standing Wave frequency of said elastic member so as to establish at least one nodal point and one antinodal point along said member, an annular ring connected to said elastic member at said antinodal point, and means for supporting said elastic member so that said annular ring is located in said bath for delivering high frequency vibratory energy to the molten metal adjacent said peripheral surface of said liner.

5. Sonic vibratory apparatus for Wetting the peripheral surface of a ferrous metal brake liner located in a bath of molten aluminum, comprising an elongated bar, a pair of counter-rotating air driven vibrators supported by one end of said bar, an annular coupling ring secured to the other end of the bar With its axis coaxial with the longitudinal axis of said bar, a source of compressed air for driving said vibrators at a resonant standing wave frequency of said bar so that at least one nodal point is located between the outer end of said bar and the point of connection between the coupling ring and the bar and the outer end of said bar is located at an antinode, and means for supporting said bar at a nodal point so that said annular ring is located in said bath for delivering high frequency vibratory energy to the molten aluminum adjacent the peripheral surface of said liner.

References Cited UNITED STATES PATENTS 3,027,694 4/ 1962 Alder 25-41 X 3,117,356 1/1964 Weber 164-48 1,947,782 2/1934 Lejeune 164-333 X 1,955,156 4/1934 Udale 188218 3,165,983 1/1965 Thomas 16495 X FOREIGN PATENTS 449,140 6/ 1948 Canada.

479,933 2/ 1938 Great Britain.

129,217 3/1959 U.S.S.R.

161,477 12/ 1962 U.S.S.R.

.T. SPENCER OVERHOLS-ER, Primary Examiner. V. K. RISING, Assistant Examiner. 

1. A METHOD OF WETTING A METAL SURFACE WITH A MOLTED METAL COMPRISING THE STEPS OF: TORSIONALLY VIBRATING AN ELASTIC COLUMN PRODUCING A STANDING WAVE VIBRATION AT THE RESONATE FREQUENCY THEREOF CAUSING ALTERNATING TORSIONAL DEFLECTIONS TO OCCUR AT OPPOSITE ENDS OF SAID COLUMN, THE DEFLECTION AT ONE END BEING GENERALLY 180 DEGREES OUT OF PHASE WITH THE DEFLECTION AT THE OTHER END AT THE RESONATE FREQUENCY, SUPPORTING SAID COLUMN AT THE NODAL POINT WHERE TORSIONAL DEFLECTION IS AT A MINIMUM, SUPPORTING A METAL BODY AT ONE END OF THE COLUMN SO THAT IT RECEIVES OSCILLATORY EXCITATIONS THEREFROM, PLACING SAID BODY WHILE IN SAID OSCILLATING CONDITION IN A CONTAINER, AND INTRODUCING MOLTEN METAL INTO THE CONTAINER TO MECHANICALLY ATTACK AND WET THE SURFACES OF SAID BODY AS A RESULT OF THE SHEARING ACTION BETWEEN THE MOLTEN METAL AND BODY SURFACES.
 3. SONIC VIBRATORY APPARATUS FOR WETTING THE SURFACE OF A FERROUS METAL ARTICLE LOCATED IN A BATH OF MOLTEN NON-FERROUS METAL, COMPRISING AN ELASTIC MEMBER, VIBRATION GENERATING MEANS CONNECTED TO SAID ELASTIC MEMBER, A SOURCE OF COMPRESSED AIR FOR DRIVING SAID VIBRATION GENERATING MEANS AT A RESONANT STANDING WAVE FREQUENCY OF SAID ELASTIC MEMBER SO AS TO ESTABLISH AT LEAST ONE NODAL POINT AND ONE ANTINODAL POINT ALONG SAID MEMBER, A COUPLING MEMBER EXTENDING FROM SAID ELASTIC MEMBER AT AN ANTINODAL POINT THEREOF, AND MEANS FOR SUPPORTING SAID ELASTIC MEMBER SO THAT SAID COUPLING MEMBER IS LOCATED IN SAID BATH FOR DELIVERING HIGH FREQUENCY VIBRATORY ENERGY TO THE MOLTEN NON-FERROUS METAL ADJACENT SAID SURFACE OF SAID ARTICLE. 